This invention relates to sound attenuating mufflers for motor vehicle exhaust systems and, in particular, to the use of cartridges formed of fibrous sound absorbent material in such mufflers. The use of cartridges of fibrous material in exhaust mufflers is shown in U.S. Pat. Nos. 2,072,961 (issued Mar. 9, 1937), 3,109,511 (issued Nov. 5, 1963), 3,112,007 (issued Nov. 26, 1963), and 3,233,697 (issued Feb. 8, 1966).